Liquid crystal display devices are flat display devices having excellent characteristics such as high resolution, thinness, light weight, and low power consumption. In recent years, a market for liquid crystal display devices has been rapidly expanding in scale due to improvement in display performance, production capacity, and competitiveness in price with other display devices.
A known method for driving liquid crystal display devices is an active matrix driving method. A liquid crystal display device driven by the active matrix driving method includes an active matrix substrate 100 as illustrated in FIG. 17. The active matrix substrate 100 includes: a plurality of scanning signal lines 116; a plurality of data signal lines 115 provided so as to cross the scanning signal lines; thin film transistors (TFTs) 112 formed adjacent to intersections of the signal lines (115, 116); and pixel electrodes 117. Each of the TFTs 112 includes: a source electrode 119 connected to one of the data signal lines 115; and a drain electrode 108 connected via a wire 107 to one of the pixel electrodes 117. Each of the scanning signal lines 116 also serves as a gate electrode of one of the TFTs 112.
The wire 107 and the pixel electrode 117 are separated by an insulating film, which has a hole. This provides a contact hole 110 for connecting the wire 107 with the pixel electrode 117. Each pixel electrode 117 is a transparent electrode made of, e.g., ITO, and transmits light (backlight) from below the active matrix substrate.
In the active matrix substrate 100, each TFT 112 is switched on (i.e., is set in a state allowing for conduction between its source electrode 119 and drain electrode 108) by a scanning signal (gate ON voltage) transmitted through a corresponding scanning signal line 116. In this state, a data signal (signal voltage) transmitted through a corresponding data signal line 115 is written, via the source electrode 119, the drain electrode 108, and a corresponding wire 107, into a corresponding pixel electrode 117. Retention capacitor (Cs) lines 118 each have a function of, e.g., preventing self-discharge of a liquid crystal layer, the self-discharge being caused while a TFT 112 is off.
In a process of producing the active matrix substrate 100, foreign objects, film residues and/or the like may cause a short circuit (leak) between the source electrode 119 and the drain electrode 108 of any TFT 112. Such a defective TFT fails to apply a normal voltage (drain voltage) to its corresponding pixel electrode 117.
A liquid crystal display device of a vertical alignment (VA) mode, for example, generally carries out a normally black display, in which it carries out a black display when no voltage is applied, while it carries out a white display when a voltage is applied. In such a liquid crystal display device, a source-drain short circuit as described above causes a voltage to be constantly applied to the pixel. This results in a pixel defect of a bright dot, which is a highly visible defect.
Such a pixel defect may be repaired by the following method of a repairing process: When a TFT 112 has a short circuit between its source electrode 119 and drain electrode 108 as indicated by X1 in FIG. 17, its corresponding wire 107 is cut, e.g., at a position indicated by X2. This electrically separates a corresponding pixel electrode 117 from the TFT 112. Further, a retention capacitor line 118 and the wire 107 are melted at a position indicated by X3 so as to be short-circuited with each other. This electrically connects the pixel electrode 117 with the retention capacitor line 118.
In consequence of the above repairing process, a voltage having a potential of a voltage of the retention capacitor line 118 is applied to the pixel electrode 117 of the defective pixel. This causes the pixel to be shown as a black dot in a case of a display method of a normally black mode, thus rendering the defective pixel less visible than when it is shown as a bright dot.